Abscisic acid biosynthesis inhibitor

ABSTRACT

Compounds represented by the following general formula (I) or salts thereof:  
                 
 
wherein R 1  represents hydrogen atom, hydroxyl group, or an alkoxy group; R 2  represents hydroxyl group or an alkoxy group which may be substituted; R 3  represents hydrogen atom or an alkyl group which may be substituted; Y represents —CH═CH— or —CH 2 —; n represents 0 or 1; Ar represents an aryl group which may be substituted or a heteroaryl group which may be substituted, which are useful as inhibitors against the abscisic acid biosynthesis and plant growth regulators.

TECHNICAL FIELD

The present invention relates to a compound having inhibitory actionagainst abscisic acid biosynthesis or a salt thereof, and also to aninhibitor against the abscisic acid biosynthesis or a plant growthregulator comprising said compound or a salt thereof as an activeingredient.

BACKGROUND ART

Abscisic acid is a plant hormone that involves in plant responses tovarious environmental stresses. For example, when a plant is sufferedfrom dry stress, abscisic acid is rapidly accumulated, and then, poreclosing and expression of stress-related genes such as rabl8, kin1, andrd29B are promoted. As for abscisic acid biosynthesis in plants, a majorpathway involves, via a carotenoid of a compound comprising 40 carbonatoms, use of xanthoxin having 15 carbon atoms as a precursor, which isgenerated by the degradation of the carotenoid, and oxidation of thehydroxyl group at the 3′-position, the isomerization of the double bondderived from the epoxy cleavage; and the oxidation of the aldehyde intocarboxylic acid. In particular, the cleavage reaction of epoxycarotenoidby dioxygenase [nine-cis-epoxycarotenoid dioxygenase (NCED)] intoxanthoxin is considered as a reaction that controls the abscisic acidbiosynthesis.

In order to elucidate physiological functions of abscisic acid, which isa plant hormone essential for plant growth, methods has been used so farwherein abscisic acid is directly applied to a plant, or wherein amutant whose gene for the abscisic acid biosynthesis is destroyed isused to analyze expressed physiological phenomena. However, by theapplication of abscisic acid, which already exists in the plant body, itis difficult to elucidate actual physiological actions of inherentabscisic acid. The methods using the mutants, which are in deficientstage of abscisic acid, are useful for investigation of the functions ofabscisic acid by comparison with wild strains in physiological phenomenaand morphologic states. However, the methods have disadvantages in thatthey are inapplicable to various plants and the abscisic acid deficientstate cannot be controlled in a desired growth period.

As a method for compensating the disadvantages of the methods availableto date, inhibitors against the abscisic acid biosynthesis can beutilized. In order to artificially obtain an abscisic acid deficientplant, agents inhibiting the biosynthesis of carotenoid, which is anintermediate of the abscisic acid biosynthesis, have already been used;however, such agents have potent whitening action, and accordingly, theyare inappropriate for investigation of an abscisic acid deficient statewithout involvement of side effects. Under these circumstances, if aspecific inhibitor against abscisic acid can be provided, various plantscan easily be introduced in an abscisic acid deficient state, andanalytical studies of abscisic acid functions can be expectedlyprogressed. In addition, an abscisic acid biosynthesis inhibitor can beutilized as a plant growth regulator which is effective for variousgrowth processes of plants. It has been reported that NDGA[4,4′-(2,3-dimethyl-1,4-butanediyl)bis-1,2-benzenediol] which is knownas a peroxidase inhibitor has inhibitory action on the abscisic acidbiosynthesis on the basis of the results of inhibitory test of poreclosing activity and the analysis of the amount of inherent abscisicacid production (Plant Physiology (1992) 99, 1258-1260).

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a compound havinginhibitory action against the abscisic acid biosynthesis. The inventorsof the present invention conducted intensive studies to achieve theforegoing object. As a result, they found that the compounds representedby the following general formula (I) or salts thereof have inhibitoryaction against the abscisic acid biosynthesis, and that they were usefulas plant growth regulators. The present invention was achieved on thebasis of these findings.

The present invention thus provides a compound represented by thefollowing general formula (I):

(wherein R¹ represents hydrogen atom, hydroxyl group, or an alkoxygroup; R² represents hydroxyl group or an alkoxy group which may besubstituted; R³ represents hydrogen atom or an alkyl group which may besubstituted; Y represents —CH═CH— or —CH₂—; n represents 0 or 1; Arrepresents an aryl group which may be substituted or a heteroaryl groupwhich may be substituted) or a salt thereof.

From another aspect of the present invention, there are provided aninhibitor against the abscisic acid biosynthesis which comprises thecompound represented by the aforementioned general formula (I) or a saltthereof as an active ingredient; an epoxycarotenoid dioxygenaseinhibitor which comprises the compound represented by the aforementionedgeneral formula (I) or a salt thereof as an active ingredient; a plantgrowth regulator which comprises the compound represented by theaforementioned general formula (I) or a salt thereof as an activeingredient; and a use of the compound represented by the aforementionedgeneral formula (I) or a salt thereof for the manufacture of theaforementioned inhibitor or the aforementioned regulator.

The present invention further provides a method for inhibiting theabscisic acid biosynthesis in a plant body, which comprises the step ofapplying the compound represented by the aforementioned general formula(I) or a salt thereof to a plant; a method for inhibitingepoxycarotenoid dioxygenase in a plant body, which comprises the step ofapplying the compound represented by the aforementioned general formula(I) or a salt thereof to a plant; and a method for regulating plantgrowth, which comprises the step of applying the compound represented bythe aforementioned general formula (I) or a salt thereof to a plant.

BEST MODE FOR CARRYING OUT THE INVENTION

As the alkoxy group represented by R¹, for example, a linear or branchedalkoxy group having 1 to about 6 carbon atoms can be used. Preferably,an alkoxy group such as methoxy group, ethoxy group and n-propoxy groupcan be used, and more preferably, methoxy group can be used. As R¹;hydrogen atom or methoxy group is preferred. As the alkoxy grouprepresented by R², which has the same definition as the above, methoxygroup can preferably be used. When the alkoxy group represented by R² issubstituted, types, numbers, and substituting positions of substituentsare not particularly limited. For example, substituents containingoxygen atom such as an alkoxycarbonyl group, carboxyl group and hydroxylgroup are preferred. As the substituted alkoxy group represented by R²,for example, an alkoxycarbonyl-substituted alkoxy group is preferred,and more preferably, methoxycarbonyl-substituted methoxy group can beused. As R², hydroxyl group, methoxy group, or methoxycarbonylmethoxygroup is preferred.

The alkyl group represented by R³, for example, a linear or branchedalkyl group having 1 to about 6 carbon atoms can be used. Preferably, analkyl group such as methyl group, ethyl group and n-propyl group can beused, and more preferably, methyl group can be used. When the alkylgroup represented by R³ is substituted, types, numbers, and substitutingpositions of substituents are not particularly limited. For example,substituents containing oxygen atom such as an alkoxycarbonyl group,carboxyl group and hydroxyl group are preferred. As R³, hydrogen atom,methyl group, or methoxycarbonylmethyl group is preferred.

Examples of the aryl group represented by Ar include phenyl group,naphthyl group and the like, and preferably, phenyl group can be used.As the heteroaryl group represented by Ar, for example, a 5-10 memberedheteroaryl group which contains one or more heteroatoms selected fromthe group consisting of nitrogen atom, oxygen atom, and sulfur atom asthe ring constituting atoms can be used. More preferably, a 5- or6-membered heteroaryl group which contains one or two nitrogen atoms oroxygen atoms as the ring constituting atoms can be used, and furtherpreferably, a 5- or 6-membered heteroaryl group which contains onenitrogen atom or oxygen atom as the ring constituting atom can be used.More specifically, pyridyl group, furyl group or the like is preferredas the heteroaryl group. When the aryl group or the heteroaryl grouprepresented by Ar is substituted, types, numbers, and substitutingpositions of substituents are not particularly limited. For example, thearyl group or the heteroaryl group is preferably substituted with 1 orabout 2 substituents such as hydroxyl groups, alkoxy groups (forexample, methoxy group), halogen atoms (for example, fluorine atom,chlorine atom and bromine atom). Preferred substituents include hydroxylgroup, methoxy group, and fluorine atom. When Ar is phenyl group, thephenyl group is preferably substituted at the 3- and/or 4-position.

The compounds represented by the general formula (I) may sometimes haveone or more asymmetric carbon atoms depending on the type of thesubstituent. Accordingly, any optical isomer in an optically pure formbased on the one or more asymmetric carbon atoms, any mixture of opticalisomers, racemates, diastereoisomers in pure forms, mixtures of thediastereoisomers, and the like fall within the scope of the presentinvention. The compounds represented by the general formula (I) maysometimes exist as base addition salts such as sodium salt and potassiumsalt, or acid addition salts such as hydrochloride, sulfate andp-toluenesulfonate. Any of these salts falls within the scope of thepresent invention. The compound in a free form or that in a form of asalt may sometimes exist as a hydrate or a solvate, and these substancesnaturally fall within the scope of the present invention.

Preferred examples of the compounds represented in the general formula(I) will be shown below. However, the scope of the present invention isnot limited to the following compounds. (I)

Compound No. R¹ R² Y R³ n Ar SY87 CH₃O— CH₃O— —CH═CH— H— 0 Ph(4-OCH₃)SY88 H— HO— —CH₂— H— 1 Ph(3,4-di-OCH₃) SY90 H— HO— —CH₂— H— 1Ph(3,4-di-OH) SY94 H— CH₃O—CO—CH₂—O— —CH₂— CH₃O—CO—CH₂— 1Ph(3,4-di-OCH₃) SY95 CH₃O— CH₃O— —CH═CH— H— 1 Ph(4-F) SY96 H— CH₃O——CH₂— CH₃— 1 Ph(3,4-di-OCH₃) SY97 CH₃O— CH₃O— —CH═CH— CH₃O—CO—CH₂— 1Ph(4-F) SY99 CH₃O— CH₃O— —CH═CH— CH₃— 1 Ph(4-F) SY106 H— HO— —CH₂— H— 14-Pyridyl SY107 H— HO— —CH₂— H— 1 3-Furyl SY109 H— HO— —CH₂— H— 1Ph(2-OH)

The compound represented by the aforementioned general formula (I) caneasily prepared by, for example, condensing the corresponding aminecompound with an aldehyde to synthesize an imine, and reducing thesynthesized imine with an appropriate reducing agent. Specific exampleswill be shown in the examples of the specification. The condensation canbe performed without solvent, and also can advantageously be preformedin suitable combination of an appropriate solvent with an acid catalyst.As the reducing agent, sodium borohydride can be used; however, thereducing agent is not limited thereto. The amine generated from thereduction can be modified by, for example, alkylation which is performedby reacting the amine with an appropriate alkyl halide in the presenceof a strong base such as sodium hydride. Preparation examples accordingto the aforementioned preparation method will be specifically shown inthe examples of the specification. Therefore, those skilled in the artcan prepare any compound represented in the general formula (I) byreferring to the aforementioned general descriptions and specificexplanations in the examples, and appropriately choosing startingmaterials, reagents, reaction conditions and the like, and if necessary,by adding suitable modifications and alterations to the aforementionedmethod.

The compounds represented by the aforementioned general formula (I) orsalts thereof have inhibitory action against the abscisic acidbiosynthesis, and are useful as, for example, active ingredients ofplant growth regulators. In addition, the compounds of the presentinvention or salts thereof can be used as specific inhibitors againstepoxycarotenoid dioxygenase. By applying the compounds of the presentinvention represented by the aforementioned general formula (I) toplants as plant growth regulators, plant growth, taking root,germination and the like can be promoted. The term “plant growthregulation” used in this specification should be construed in itsbroadest sense, including, for example, regulation of plant elongation,pollen growth regulation, retention of flower freshness, enhancement ofthe plant anti-stress property against stresses such as heat, dryness,coldness, diseases and the like, weed control by regulation ofreproduction, suppression of plant retrogradation, control ofhypertrophy of root. The compounds of the present invention or saltsthereof can also be used as, for example, biochemical reagents in thestudies for elucidation of the biosynthetic path or the functions ofabscisic acid.

The inhibitor against the abscisic acid biosynthesis, the specificinhibitor against epoxycarotenoid dioxygenase, and the plant growthregulator provided by the present invention can be formulated, forexample, as an agricultural composition by using formulation additiveswell known in the art. Forms of the agricultural composition are notparticularly limited, and any form that can be used in the art may bechosen. For example, compositions in the forms of emulsions, liquids,oils, water soluble powders, wettable powders, flowables, powders,subtilized granules, granules, aerosols, fumigants, pastes and the likecan be used. The methods for manufacturing the agricultural compositionare also not particularly limited, and any method available to thoseskilled in the art can be appropriately employed. As the activeingredient of the inhibitors of the present invention, two or more ofthe compounds represented by the aforementioned general formula (I) orsalts thereof may be used in combination. Further, other activeingredients of agricultural chemicals such as insecticides, fungicides,insecticidal and fungicidal agents, herbicides and the like may bemixed. Methods of application and doses of the inhibitors of the presentinvention can be suitably chosen by those skilled in the art dependingon conditions including a purpose of application, a dosage form, a plotto be treated and the like. The concentration to obtain the optimalaction can properly be decided by those skilled in the art by referringto the following examples.

EXAMPLES

The present invention will be explained more specifically with referenceto examples. However, the scope of the present invention is not limitedto the following examples.

Example 1 Compound SY109 [4-[2-(2-hydroxy-benzylamino)-ethyl]-phenol]

(a) Synthesis of Compound SY108[4-{2-[(2-hydroxy-benzylidene)-amino]-ethyl}-phenol]

4-Hydroxyphenethylamine (1.37 g, 10 mmol) and 2-hydroxybenzylamine (1.22g, 10 mmol) were reacted with heating under reflux in toluene. After thereaction was terminated, the solvent was evaporated under reducedpressure, and purification was performed by silica gel columnchromatography (hexane/ethyl acetate) to obtain the desired imine. Yield2.15 g.

¹H-NMR (MeOH-d₆) δ 7.25 (1H, s), 7.36-7.23 (2H, m), 7.06 (2H, d), 6.85(2H, m), 6.72 (2H, d), 4.90 (2H, br s), 3.82 (2H, t), 2.92 (2H, t)

(b) Synthesis of Compound SY109

Compound SY108 (1.2 g, 5 mmol) was dissolved in ethanol (20 ml), andadded with an excess amount of sodium borohydride with stirring. Theprogress of the reaction was monitored by using thin layerchromatography. After the starting material disappeared, the reactionwas terminated, and water (50 ml) was added to the reaction mixture. Theethanol was evaporated under reduced pressure, and the aqueous layer wasextracted three times with ethyl acetate, and then the extract wasdried, concentrated, and purified by using silica gel columnchromatography (chloroform/ethyl acetate) to obtain the desiredcompound. Yield 0.8 g.

¹H-NMR (CDCl₃+Acetone-d₆) δ 7.08 (1H, t), 6.97 (2H, d), 6.91 (2H, d),6.74 (2H, d), 6.76-6.67 (2H, m), 3.91 (2H, s), 2.87 (2H, t), 2.72 (2H,t)

Example 2 Compound SY94[{(3,4-dimethoxy-benzyl)-[2-(4-methoxycarbonylmethoxy-phenyl)-ethyl]-amino}-aceticAcid Methyl Ester]

(a) Compound SY73[4-{2-[(3,4-dimethoxy-benzylidene)-amino]-ethyl}-phenol]

Compound SY73 was obtained in the same manner as in Example 1(a). ¹H-NMR(Acetone-d₆) δ 8.14 (1H, s), 7.46 (1H, s), 7.19 (1H, d), 7.09 (2H, d),6.99 (1H, d), 6.77 (2H, d), 3.86 (3H, s), 3.85 (3H, s), 3.74 (2H, t),2.87 (2H, t)

(b) Synthesis of Compound SY88[4-[2-(3,4-dimethoxy-benzylamino)-ethyl]-phenol]

Compound SY88 was obtained in the same manner as in Example 1(b). ¹H-NMR(CDCl₃+Acetone-d₆) δ 6.98 (2H, d), 6.73 (1H, s), 6.67-6.63 (4H, m), 3.73(3H, s), 3.72 (3H, s), 3.61 (2H, s), 2.75-2.70 (2H, m), 2.64-2.60 (2H,m)

(c) Synthesis of Compound SY94

Compound SY88 (287 mg, 1 mmol) was dissolved in dry dimethylformamide (3ml), and the solution was added with 1.3 equivalents of sodium hydrideand stirred for 10 minutes. Then, 1.3 equivalents of brominated methylacetate were added, and the reaction was carried out at room temperaturefor 4 hours. After the reaction was terminated, the reaction mixture waspoured into water (20 ml) and extracted three times with ethyl acetate.The extract was dried, concentrated, and purified by silica gel columnchromatography to obtain the desired compound. Yield 125 mg. ¹H-NMR(CDCl₃) δ 7.08 (2H, d), 6.87 (1H, s), 6.78 (2H, d), 6.76 (2H, m), 4.59(2H, s), 3.85 (3H, s), 3.83 (3H, s), 3.78 (3H, s), 3.75 (2H, s), 3.67(3H, s), 3.35 (2H, s), 2.80-2.85 (2H, m), 2.76-2.71 (2H, m)

Example 3

The following intermediate compounds and the compounds of the presentinvention were prepared in the same manner as in Examples 1 and 2.

-   Compound SY72    [4-{[2-(4-hydroxy-phenyl)-ethylimino]-methyl}-benzene-1,2-diol    ¹H-NMR (Acetone-d₆+DMSO-d₆) δ 8.03 (1H, s), 7.31 (1H, s), 7.06 (2H,    d), 6.90 (1H, d), 6.80 (1H, d), 6.72 (2H, d), 3.68 (2H, t), 3.15    (3H, br s), 2.82 (2H, t)-   Compound SY76 [3-(3,4-dimethoxy-phenyl)-prop-2-ene-1-ol] ¹H-NMR    (Acetone-d₆) δ 7.08 (1H, s), 7.07-6.87 (2H, m), 6.54 (1H, d), 6.29    (1H, td), 4.23 (2H, d), 3.84 (3H, s), 3.80 (3H, s), 3.05(1H, br s)-   Compound SY78 [3-(3,4-dimethoxy-phenyl)-propenal] ¹H-NMR (CDCl₃) δ    7.44 (1H, d), 7.17 (1H, d), 7.09 (1H, s), 6.93 (1H, d), 6.63 (1H,    dd), 3.96 (3H, s), 3.95 (3H, s), 9.68 (1H, d)-   Compound SY83    [[3-(3,4-dimethoxy-phenyl)-allylidene]-(4-methoxy-phenyl)-amine]    ¹H-NMR (Acetone-d₆) δ 8.37 (1H, s), 7.33 (1H, s), 7.32-7.15 (4H, m),    7.05-6.94 (4H, m), 3.93 (3H, s), 3.87 (3H, s), 3.83 (3H, s)-   Compound SY93    [[3-(3,4-dimethoxy-phenyl)-allylidene]-(4-fluoro-benzyl)-amine]    ¹H-NMR (Acetone-d₆) δ 8.19 (1H, d), 7.42-7.26 (3H, m), 7.15-6.83    (6H, m), 4.67 (2H, s), 3.89 (3H, s), 3.85 (3H, m)-   Compound SY104 [4-{2-[(pyridin-4-ylmethylene)-amino]-ethyl}-phenol]    ¹H-NMR (Acetone-d₆) δ 8.68 (2H, d), 8.26 (1H, s), 7.67 (2H, d), 7.09    (2H, d), 6.76 (2H, d), 3.86 (2H, t), 2.94 (1H, br s), 2.91 (2H, t)-   Compound SY105 [4-{2-[(furan-3-ylmethylene)-amino]-ethyl}-phenol]    ¹H-NMR (Acetone-d₆) δ 8.19 (1H, s), 7.91 (1H, s), 7.59 (1H, s), 7.06    (2H, d), 6.81 (1H, s), 6.75 (2H, d), 3.71 (2H, t), 2.89 (1H, br s),    2.843 (2H, t)-   Compound SY87    [[3-(3,4-dimethoxy-phenyl)-allyl]-(4-methoxy-phenyl)-amine] ¹H-NMR    (MeOH-d₆) δ 7.44 (2H, d), 7.14-6.94 (5H, m), 6.78 (1H, d), 6.19 (1H,    td), 4.89 (1H, br s), 4.14 (2H, d), 3.87 (9H, s)-   Compound SY90    [4-{[2-(4-hydroxy-phenyl)-ethylamino]-methyl}-benzene-1,2-diol]    ¹H-NMR (MeOH-d₆) δ 7.09 (2H, d), 7.01 (1H, s), 6.87 (2H, m), 6.79    (2H, d), 4.95 (4H, br s), 4.06 (2H, s), 3.17 (2H, m), 2.81 (2H, m)-   Compound SY95    [[3-(3,4-dimethoxy-phenyl)-allyl]-(4-fluoro-benzyl)-amine] ¹H-NMR    (MeOH-d₆) δ 7.58 (2H, m), 7.27-7.05 (4H, m), 6.97 (1H, d), 6.84    (lH,d), 6.20 (1H, td), 4.89 (1H, br s), 4.26 (2H, s), 3.88 (3H, s),    3.87 (3H, s), 3.84 (2H, d)-   Compound SY96    [(3,4-dimethoxy-benzyl)-[2-(4-methoxy-phenyl)-ethyl]-methyl-amine]    ¹H-NMR (CDCl₃) δ 7.12 (2H, d), 7.86 (2H,d), 6.86 (3H, m), 3.89 (3H,    s), 3.87 (3H, m), 3.80 (3H, s), 3.51 (2H, s), 2.82-2.77 (2H, m),    2.65-2.60 (2H, m), 2.30 (3H, s)-   Compound SY97    [[[3-(3,4-dimethoxy-phenyl)-allyl]-(4-fluoro-benzyl)-amino]-acetic    acid methyl ester] ¹H-NMR (CDCl₃) δ 7.34 (2H, m), 7.03-6.87 (4H, m),    6.79 (1H, d), 6.47 (1H, d), 6.22-6.12 (1H, td), 3.89 (3H, s), 3.86    (3H, s), 3.77 (2H, s), 3.66 (3H, s), 3.38 (2H, d), 3.34 (2H, s)-   Compound SY99    [[3-(3,4-dimethoxy-phenyl)-allyl]-(4-fluoro-benzyl)-methyl-amine]    ¹H-NMR (CDCl₃) δ 7.31 (2H, m), 7.05-6.97 (4H, m), 6.82 (1H, d), 6.48    (1H, d), 6.22-6.12 (1H, td), 3.90 (3H, s), 3.88 (3H, s), 3.52 (2H,    s), 3.17 (2H, d), 2.23 (3H, s)-   Compound SY106 [4-{2-[(pyridin-4-ylmethyl)-2-amino]-ethyl}-phenol]    ¹H-NMR (Acetone-d₆) δ 8.47 (2H, d), 7.33 (2H, d), 7.05 (2H, d), 6.75    (2H, d), 3.83 (2H, s), 2.88 (2H, br s), 2.82-2.77 (2H, m), 2.74-2.69    (2H, m)-   Compound SY107 [4-{2-[(furan-3-ylmethyl)-amino]-ethyl}-phenol]    ¹H-NMR (Acetone-d₆) δ 7.45 (2H, d), 7.05 (2H, d), 6.75 (2H, d),    6.42(1H, s), 3.63 (2H, s), 2.90 (2H, br s), 2.81-2.76 (2H, m),    2.72-2.61 (2H, m)

Test Example 1

The inhibitory action against epoxycarotenoid dioxygenase was studied.The test was carried out according to the method described in The PlantJournal (2001) 27(4), 325-333. As a result, it was demonstrated thatNDGA [4,4′-(2,3-dimethyl-1,4-butanediyl)bis-1,2-benzenediol] completelyinhibited the cleavage reaction of neoxanthin by NCED at theconcentration of 100 μM. Accordingly, it was concluded that thiscompound exhibits inhibitory activity against the abscisic acidbiosynthesis by inhibiting NCED.

Test Example 2

Inhibitory tests against pore closing were carried out by using theaforementioned compounds. In these tests, plants in the state that theirpores are open are treated with the compounds, and closings of the poresare examined when the plants are transferred into a mannose solution ofhigh concentration to make the pores closed. Pore closing is caused bythe effect of abscisic acid biosynthesized in the body of a plant thathas detected the change of the mannose concentration. The test wascarried out according to the method described in the literature of PlantPhysiology (1992) 99, 1258-1260 and by using spinach as a material.

As a result, Compounds SY109, 87, 94, 99, 96, 97, and 95 were found tohave potent inhibitory activities against pore closing. When the plantstreated with these compounds were added with abscisic acid, pores of theplants closed, whereas when the plants treated with NDGA were added withabscisic acid, pores of the plant did not close. These results areconsidered to be derived from an undesired influence of NDGA on someactions of plants other than the abscisic acid biosynthesis to exert thetoxicity. From these results, it was concluded that the compounds of thepresent invention are more specific inhibitors against the abscisic acidbiosynthesis than NDGA.

Test Example 3

The NCED inhibitory activity of the compounds of the present inventionwas studied. As a result, each of the compounds, SY109, 87, 94, 99, 96,97, and 95, was found to have 30 to 100% NCED inhibitory activity at theconcentration of 100 μM.

Test Example 4

The compounds of the present invention were applied to plant bodies.Hypocotyls of Mung bean on the 6th-day after seeding, that were grown at25° C., were cut in water with razor, and the hypocotyl parts weresoaked by 2 cm in solutions of the compounds at a given concentration.On the 6th day after the soaking, the lengths of the roots weremeasured. The following results were shown as an average length perroot. TABLE 2 Compound Length (cm) SY87 0.6 SY88 >0.1 SY90 >0.1 SY94 2.1SY95 0.6 SY96 1.5 SY97 0.7 SY99 0.4 SY106 >0.1 SY107 >0.1 SY109 1.5Control >0.1

Test Example 5

The germination rate of seeds of barley, which had significantly loweredgermination rate, was compared between the seeds after treatment withthe compounds and the seeds without the treatment. In the test, 2 sheetsof filter paper were placed in a 15 cm laboratory dish, and each of thetest solutions of the compounds at a given concentration (10 ml) wasadded to the dish, and 100 seeds were put on the paper and culturedunder a light at 25° C. Ratios of germinated seeds were calculated afterone week. TABLE 3 Compound Germination rate (%) SY87 40 SY88 8 SY90 12SY94 52 SY95 29 SY96 21 SY97 18 SY99 15 SY106 9 SY107 10 SY109 35Control 9Industrial Applicability

The compounds of the present invention have inhibitory action againstthe abscisic acid biosynthesis, and are useful as plant growthregulators for promoting plant growth, taking root, germination and thelike.

1. A compound represented by the following general formula (I) or a saltthereof:

wherein R¹ represents hydrogen atom, hydroxyl group, or an alkoxy group;R² represents hydroxyl group or an alkoxy group which may besubstituted; R³ represents hydrogen atom or an alkyl group which may besubstituted; Y represents —CH═CH— or —CH₂—; n represents 0 or 1; Arrepresents an aryl group which may be substituted or a heteroaryl groupwhich may be substituted.
 2. An inhibitor against an abscisic acidbiosynthesis which comprises the compound represented by the generalformula (I) according to claim 1 or a salt thereof as an activeingredient.
 3. An epoxycarotenoid dioxygenase inhibitor which comprisesthe compound represented by the general formula (I) according to claim 1or a salt thereof as an active ingredient.
 4. A plant growth regulatorwhich comprises the compound represented by the general formula (I)according to claim 1 or a salt thereof as an active ingredient.